Сокращение от rolling on the floor laughing, по русски - валяюсь на полу от смеха. Русскоязычный аналог - "пацтолом".
That's so funny! ROFL!
Вариации:
ROTFL (Rolling On The Floor Laughing)
ROFLMAO (Rolling On the Floor Laughing My Ass Off)
ROFLMAOSTC (Rolling On The Floor Laughing My Ass Off Scaring The Cat).
